Reproductive Phenology and Allocation in Rubus palmatus var. coptophyllus in the Understory of a Pinus densiflora Stand

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1 ~;tff.t:mmw Bull. For. & For. Prod. Res. lnst. No. 367, Reproductive Phenology and Allocation in Rubus palmatus var. coptophyllus in the Understory of a Pinus densiflora Stand By SUZUKI, Wajirou l Summary : Flowering and fruiting phenology, and reproductive allocation were investigated in a Rubus palmatus var. coptophvllus population which developed on the forest floor of an 86-year old Pinus densiflora stand. About 7% of the suckers in the population ranged from 6-15 years. and the average sucker age was 1.6 years. Flowers began to open on the floricane in the middle of April. and fruits ripened one month later. There were allometric relationships between the cane size and the number of flowers and fruits per cane. According to these regression lines, as the cane size increased, the fruit/flower ratio increased. The mean value of reproductive allocation (RA) in the fruiting stage was 4.6%, which was three times as much as that of the flowering stage. There were no significant re lationships between sucker biomass and RA in both stages. Reproductive outputs increase with increasing sucker size. independent of RA. I, Introduction Energy investment for sexual reproduction, as well as the number of offsprings produced, is an important factor for understanding adaptive strategies of plants (HARPER, 1967; PIANKA, 197). GRE, NRE and CRE as measures of reproductive effort (RE) were proposed by HARPER and OGDEN (197), and the reproductive effort was measured in many herbaceous plants (KAWANO, 1975; NEWELL and TRAMER, 1978; OGDEN, 1974). These studies showed that RE or reproductive allocation (RA) vary among species, and are greatly affected by the growing conditions. such as population density. soil fertility, light and water conditions (OGDEN, 1974; PITELKA et al.. 198; KAWANO and HAYASHI, 1977: HARA et al., 1988). RA (sexual reproductive allocation) values in some Rubus species belonging to a "nonintegrated clonal" plant (PITELKA and ASHMlit\, 1985) were investigated (ABRAHA~1SON, 1975a and b; NARUHASHI and KOBAYASHI, 1982). However, RA values of integrated clonal Rubus species, the so-called "underground branching" type (Sl'Zl'KI. 1987), have not been measured in detail, because of difficulty in investigating the underground parts of a clone individual without destruction (NARl'HASHI and SATOMI, 1972; SUZliKI, 199). In many integrated clonal plants, ramets composing a clone become independent with increasing age (PITELKA and ASHMliN, 1985). Moreover, according to previous studies by this author about integrated clonal Rubus species (SUZliKI, 1989 and 199), the suckers composing a clone individual are independent from each other for reproduction as well as vegetative growth, in spite of be connected with perennial underground runners. These results suggest the possibility of considering reproductive ecology at sucker level for integrated clonal Rubus species. In a previous paper (StrWKI, 1987). the structure and seed production of R. palmatus var. coptophyllus populations under different light conditions were critically described. Received September (11 Tohoku Research Center HWr-14 Forestry Technology -14

2 -54- In this study. flowering and fruiting phenologies of Rubus palmatus var. coptophyllus. one of the Rubus types mentioned above. the sucker size structure of a well-developed population and RA values of this species at the sucker level were investigated. RA variation among some Rubus species in relation to growth habitats was then discussed from the aspect of reproductive ecology_ 2. Materials and Methods The field for this study is in a plantation of Pinus densiflora approximately 86 years old located in the Takizawa-mura (Lat.39o 45'. Long.l41" 15' ). Iwate Prefecture. The R. palmatus var. coptophyllus population had developed well on the forest floor of this stand, and other main dominant species composing undergrowing vegetation were Sasa nipponica and Lonicera grarilipes. The light conditions just above the undergrowth were relatively good, in spite of crown closure, about 6% in relative illuminance. A study quadrat (2m X 2m) was established in the population of this Rubus species. and five suckers were chosen in order to investigate the reproductive phenology. On each sucker chosen, the number of leaves. flowers and fruits on the floricane (second-year-cane) were counted. The length of the primocane newly sprouting from the stool was measured and the number of leaves on the primocane was counted every week from April to December, In both the flowering and fruiting stages. 2 suckers of various sizes, including underground organs within 15cm around the center of the stool, were harvested to estimate RA around the study quadrat. The diameter at the cane base (D ) and cane height (H) were measured. and the number of flowers and fruits were counted in order to establish the relationships between cane size and flower and fruit production. Each sucker was divided into sexual reproductive organs (flowers or fruits), above -ground parts without flowers or fruits, and underground organs. These were dried in a ventilated oven for 72 hours at 8'C and weighed. One of the life history characteristics of R. palmatus var. coptophyllus is the short life span of aboveground-canes. for one and a half years. and the alternating of above-ground parts every year (SliZUKJ, 1987). A new above-ground cane (primocane. A in Photo.l) sprouts from the stool every year. In the next year. the primocane becomes floricane (B in Photo.l). and produces flowers and fruits. After fruiting, it dies in the same year (withered cane. C in Photo.l). However. a new primocane sprouts from the stool at the same time. replacing the floricane. Thus. the number of traces of above-ground canes having sprouted on the stool was counted to estimate sucker age. Another study quadrat (2m X 4m) was established in the same population in 199, and all suckers appearing in the quadrat were harvested. including the underground organs. The Do and H of all canes, both living and withered were measured, and the number of cane traces on the stool were counted in order to determine the population structure and its dynamics.

3 Reproductive traits of a Rubus species (SUZUKI) Results 3.I Population structure The R. palmatus var. coptophyllus population in this study was mostly composed of old suckers of more than 6 years. About 7% of the suckers in the population were aged between 6-15 years on the sucker age-class (Table 1 ). The oldest sucker in this population was more than 2 years old. and the youngest ones were those formed in the investigated year by underground branching (SUZUKI, 1987). The average sucker age was 1.6 years. The number of canes appearing in the population and their size-class distribution did not change much during the past three years (fig.l). There were no significant relationships between sucker age and sucker biomass (r=4: n.s. at 5%). 3.2 Vegetative and reproductive phenology The leaves of the floricane of R. palmatus var. coptophyllus sprouted rapidly in April, increasing by about 8% in the number. and reached the maximum number in the middle of May. Following this, the amount of leaves remained at the 9% level of the maximum until with all the leaves being shed gradually from September to November as the cane withered (Fig.2). On the other hand. a new above-ground cane (primocane) began to sprout in the middle of May. and continued to grow until September. As the primacane grew. the number of leaves on it increased rapidly, and reached its maximum in the middle of September. when the primocane stopped growing. The primocane began to shed its leaves, from the middle of October until all leaves shed in November (Fig.2). The floricane as an above-ground part was alternated with the primocane, on account of withering. Alternation required about six months. Flowers began to open on the floricane in the middle of April. About one month after flowering, this Rubus species fruits. However. about 45% of the flowers failed to fruit (Fig.2). This failure was largely due to the predators, mainly insects, while other reasons are unknown. Both flowering and fruiting seasons were short. less than two weeks. However. some fruits did not drop to the ground until they had completely dried on the cane. 3.3 Flower and fruit production There were allometric relationships between the cane size and the number of flowers and fruits produced per cane (Fig.3). The regression line at the fruiting stage significantly differed from that at the flowering stage (at the 5% level. t-test). The number of fruits per cane was lesser than that of the flowers in the same size. According to these regression lines, the number of fruits was about 5% of flowers for canes of 5 cm 3 in D "H of canes, and about 8% for those of 2 cm 3. That is. as the cane size increased. the fruit/flower ratio increased. 3.4 RA in the flowering and fruiting stage In this study. RA was estimated as the ratio of reproductive organs (flowers or fruits) to the sucker Table 1. Age-class distribution of suckers (per 8m 2 ) Age-class( year) Total

4 N=34 1 C'ls " :;; '-' ~ :;;.. E ::l z 1989 N= N= Cane size-class D 2 H ( crn 3 ) Fig. 1. Cane size-class distribution of the population of R. palmatus var. coptophyllus biomass. including subterranean parts. RA varied from.5 to 3.5% in the flowering stage. and from 1. to 8.5% in the fruiting stage. The mean value of RA in fruiting stage was about 4.6%. which was three times as much as that of the flowering stage (Fig.4). There was no significant relationship between the total dry weight of suckers and RA (n.s. at 5%). 4. Discussion The population of R. palmatus var. coptophyllus. here under consideration, developed well on the forest floor of crown closed P. densiflora. and was mainly composed of old suckers. with an average sucker age of 1.6 years. Stool longevity was negatively correlated with shoot height and sucker density. indicating sucker vigor in R. fruticosus and R. idaeus (PELOLIZAT and LEVACHER, 1981; WHITNEY, 1978). NYBOM (1987) reports a similar relationship between shoot height and short depletion time, turnover being quicker in vigorously growing stands of R. nessensis. According to these reports, sucker age structure in this population may be caused by low vegetative sucker production under unfavorable growing conditions caused by the crown closure of the canopy trees. On the other hand, size-class structure of above-ground canes in the population had not changed in the past three years (Fig.l). These results suggest that this population was very stable in sucker number and size structure. in spite of increasing sucker age. Flowering of this Rubus species occurs simultaneously in late April. before all the floricane leaves have been expanded (Fig.2). Flowering with these phenological characteristics may attract many insects

5 Reproductive traits of a Rubus species (SCZt:KI) -57- FL 1 *- c: o: "" c: o; s Q)... Q) c "" 5 u... Q)... June Sept. Calendar date Fig. 2. Seasonal changes in number of leaves and fruits. and length of primocane of R. palmatus var. coptophyllus Open circles. leaf of primocane; filled circles, leaf of floricane; open circles with spot. fruits; double circles. growth pattern of primocane; FL, flowering; FR. fruiting. Amounts are expressed as percentages of the maximum quantities. as pollinators, and make fertilization more efficient (HANDEL, 1983). After flowering, unripe green fruits grow. with about 55% of ripening. The failure of fruiting can be attributed to predator activity. since some beetles such as Byturus atricollis. which prey on the flowers were observed (unpublished data). On the other hand. it was found that there was a difference in the ratio of fruits to flowers produced per cane between the open-site and closed-site population of this species (SUZUKI, 1989). These results suggest that many factors. such as resource and pollinator limitation as well as predator activity, are closely related to fruit production. The RA value of R. palmatus var. coptoph_vllus investigated on Mt. Tsukuba. about 5 km south of Takizawa. was about 5. 7 ± 1.2% in the fruiting stage (StrZliKI, 199). slightly larger than that in the present study. The difference in RA between the two sites may be due to the different developing stage of each population. That is. the population on Mt. Tsukuba had been developed on an open site, while the population in the study was on a closed site. Such trends in the flower and fruit production are noted between open- and closed-site populations of this species (SliZUKI, 1989). NARl'HASHI and TERACJ (1978) reported that RA at the clone level of R. hirsutus. belonging to the "underground branching" type, was only 1.97% in the fruiting stage. RA at sucker level was 5.1% in R. idaeus in the fruiting stage (SUZUKI, unpubl.). On the other hand, some Japanese native Rubus species be-

6 -58- ~l-f> Z: fl-lijf5e pjflijf5l;fji i!f ~367~ " u ;:: ;; c.. f.:::,g".cl z / Do 2 H (cm 3 ) 5 * 1 -~ " u..s o; '" b u.g 5. "" I 5 ~ d' o o co 1 I I 1 5 dill 3 D 2 H I em") Fig. 3. Allometric relationships between cane size and number of flowers and fruits. Fig. 4. Relationships between sucker bio mass and RA (Reproductive allocation) Open circles. flowering stage; filled circles. fruiting stage. A. logy= log X lr=.926) B, log Y= ogX(r=.936) Open circles. at flowering stage; filled circles. at fruiting stage. longing to the "stepping stone" type showed RA values ranging from.5-1.6% in the flowering stage and.8-2.9% in the fruiting stage (NARliHASlll and KOBAYASlll, 1982). However, RA variation among the populations was affected by habitat conditions. such as light conditions and/ or population density (ABRA HAMSON, 1975). Although RA values in the flowering stage in R. palmatus var. coptophyllus were comparatively con stant with increasing sucker biomass. RA values at the fruiting stage varied widely. independent of sucker size (Fig. 4 ). As there were fundamentally allometric relationships between the dry weight of reproductive organs and total sucker biomass in both flowering and fruiting stages (SUZUKI, 1987; 199), RA variation in the fruiting stage was caused by the accidental events such as pradation, in the process of fruiting on each sucker. In addition, fruit weight variation ranging from.6 to.16g (mean dry weight per fruit =.9 ±.2g) may affect the RA values. Acknowledgments I am grateful to Prof. S. KAWANO of Kyoto University, for his encouragement and suggestions during this study. I wish to express my cordial thanks to Dr. T. NAKASHIZUKA, Forestry and Forest Products Re search Institute, for his critical review of the manuscript. My thanks are also due to Mrs. K. T AKANO and Mrs. K. SEKIMURA for their assistance in the field study, and to the lwate Forestry Company for the courtesy extended to me in providing the study site.

7 Reproductive traits of a Rubus species (SUZUKI) -59- References ABRAHAMSON. W.G.: Reproductive strategies in drewberries. Ecology (1975) HAI\IJEL. S.N.: Pollination ecology, plant population structure, and gene flow. In: Pollination Biology (Real. L..ed.) Academic Press. Orlando (1983) HARA, T.. KAWANO, S. and :-.Lv;AI, Y.: Optimal reproductive strategy of plants. with special reference to the modes of reproductive resource allocation. Pl. Sp. Bioi (1988) HARPICR, J.L.: A Darwinian approach to the plant ecology.]. Ecology (1967) and OGDEI\, ].: The reproductive strategy of higher plants. I. The concept of strategy with spe cia! reference to Senecio vulgaris L. J. Ecology (197) KAWANO. S.: The productive and reproductive biology of flowering plants II. The concept of life history strategy in plants. J. Coli. Lib. Arts. Toyama L'niv. 8, (1975) ---- and HAYASHI. S.: Plasticity in growth and reproductive energy allocation of Coix Ma-yuen Ro man. cultivated at varying density and nitrogen levels. J. Coli. Lib. Arts. Toyama Univ. 1, (1977) ~ARliHASHI, N. and KoBAYASIII, :-.1.: Seasonal growth cycles and dry matter economy of four Rubus species (Rosaceae). J. Phytogeo. and Tax. Vol.3, (1982) and TERAO, K.: Seasonal changes in the propotional distributions of dry matter into various organs of Rubus hirsutus. J. Phytogeo. and Tax. Vol (1978) NEWELL, S.J. and TRAMER, E.J.: Reproductive strategies in herbaceous plant communities during succes sion. Ecology (1978) NYBm1. H.: A demographic study of the apomictic blackberry.rubus nessensis (Rosaceae). Nord. J. Bot (1987) OGDEN, ].: The reproductive strategy of higher plants II. The reproductive strategy of Tussilago farfara L. J. Ecology (1974) PHELO!IZAT, R. and LEVACHER, P.: Strategie adaptative de Ia ronce (Rubus fruticosus L.) dans des conditions differentes du milieu nature!. Bull. Soc. Bot. France. Letters Bot (1981) PIANKA. E.R.: On r and K-selection. Amer. Nat. 14, (197) PITELKA, L.F. and AsiiM\11\, J.W.: Physiology and integration of ramets in clonal plants. In: Population Biology and Evolution of Clonal Organisms (Jackson J.B.C., Buss. L.W. and Cook, R.E., ed.) , Yale University Press. New Haven and London (1985). STANTON, D.S. and PECKENHAM, M.O.: Effects of light and density on resource allocation in a forest herb, Asteracuminatus (Compositae). Amer. J. Bot (198) Sl'Zl'KI. W.: Comparative ecology of Rubus species (Rosaceae). I. Ecological distribution and life history characteristics of three species. R. palmatus var. coptophyllus. R. microphyllus and R. crataegifo!ius. Pl. Sp. Bioi (1987) The structure and seed production of two populations of Rubus palmatus var. coptophyllus under different light conditions. J. Jpn. For. Soc (1989) Comparative ecology of Rubus species (Rosaceae). II. Reproductive characteristics of three Rubus species, R. Palmatus var. roptophyllus, R. microphyllus and R. crataegifolius. Pl. Sp. Bioi (199) WHITNEY, G,.G.: A demographic analysis of Rubus idaeus L. and Rubus pubescens Raf.: the reproductive traits and population dynamics of two temporally isolated members of the genus Rubus. Ph.D. thesis, New Haven (Unpubl.)

8 森林総合研究所研究報告第 367 号アカマツ林床におけるモミジイチゴの繁殖季節相と繁殖分配鈴木和次郎 (1) 擁要 86 年生アカマツ人工林の林床に発達するモミジイチゴ個体群において, 開花結実の繁殖季節相と繁殖への物質分配を調査した個体群を構成するサッカー ( 株個体 ) の約 7% は 6-15 年生であり, サソカーの平均齢は 1.6 年であった開花は, 2 年生地上茎において 4 月中旬に始まり, 果実は 1 か月後に成熟した地上茎当りの開花結実数と茎サイズの間には相対成長関係が認められたこれらの回帰直線から, 茎サイズが大きくなるにしたがって, 果実数 / 開花数の値は増加した結実期における RA ( 繁殖器官への物質分配率 ) の平均値は 4.6% で, この値は開花期の 3 倍に当たったまた, 雨時期の RA とサッカーのバイオマス量との間には明らかな関係は認められなかった繁殖体 ( 種子 ) 数は, RA とは無関係にサッカーサイズが増大するにしたがって増加した 1992 年 9 月 7 H 受環,j\ 東北支所

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